1. Field of the Invention
This invention relates to a scanning and projecting device to form a distortion-free image on a flat surface to be scanned by the use of a light deflector such as a rotary type reflecting mirror like a polygonal mirror, or a rotating-and-vibrating type reflecting mirror like a galvano-mirror (both types of the reflecting mirrors will hereinafter be called generally "rotary reflecting mirror").
2. Description of the Prior Arts
There have so far been proposed various types of devices for projecting an image on a flat surface to be scanned by using a rotary reflecting mirror. As one of image projecting methods for such projecting device, two image forming optical systems are arranged with a rotary reflecting mirror being interposed therebetween, and parallel light beams are scanned by these two image forming optical systems and the rotary reflecting mirror.
FIGS. 1 and 2 of the accompanying drawing illustrate one embodiment of the image projecting device using such scanning system, in which a light beam from a scanning plane 1 is rendered a parallel light beam by a first image forming lens 2, having one of its focal planes on the scanning plane 1, and is deflected by a rotary reflecting mirror 3. This deflected parallel light beam will then be focussed on a focal plane 5 by a second image forming lens 4. Accordingly, a position P on the scanning plane 1, which is to be focussed on a fixed point P' on the plane 5, moves with rotation of the rotary reflecting mirror 3.
In such image projecting optical system, as the scanning position P on the scanning plane 1 changes with rotation of the rotary reflecting mirror 3, there takes place changes in the image forming magnification in both the scanning direction (along the plane of the drawing sheet) and the direction perpendicular to the scanning direction (normal to the drawing sheet). Further, the changes in the image forming magnification differ in the ratio thereof between the scanning direction and the direction orthogonal thereto. On account of this change in the image forming magnification, therefore, the image of the scanning plane 1 to be focussed on the fixed point P' on the focal plane 5 is distorted.